High efficiency power amplifier power architecture

ABSTRACT

A distributed power converter is for use with an RF power amplifier and includes a primary converter connected to an input voltage and configured to provide a regulated DC intermediate voltage that is galvanically isolated from the input voltage. Additionally, the distributed power converter also includes a secondary regulator connected galvanically to the regulated DC intermediate voltage and configured to generate a regulated DC supply voltage for at least a portion of the RF power amplifier. In another aspect, a method of operating a distributed power converter is for use with an RF power amplifier and includes providing a regulated DC intermediate voltage that is galvanically isolated from an input voltage and generating a regulated DC supply voltage for at least a portion of the RF power amplifier that is galvanically connected to the regulated DC intermediate voltage.

CROSS-REFERENCE TO PROVISIONAL APPLICATION

This application claims the benefit of U.S. Provisional Application No.61/178,050, filed by Michael J. Model, on May 14, 2009, entitled “HighEfficiency Power Amplifier Power Architecture” commonly assigned withthis application and incorporated herein by reference.

TECHNICAL FIELD

The present disclosure is directed, in general, to power conversion and,more specifically, to a distributed power converter and a method ofoperating a distributed power converter.

BACKGROUND

Power converters are used in many important current applications. Incell phone applications, for example, a single direct current to directcurrent (DC/DC) converter may provide a DC supply voltage to a pluralityof separate radio frequency (RF) power amplifiers associated withtransmission from a base station to user equipment. This common sourceof DC supply voltage is shared between the plurality of RF poweramplifiers employing a common ground connection. Each of the pluralityof RF power amplifiers often provides different power gains as afunction of different values of DC supply voltage. The common DC supplyvoltage is typically adjusted to accommodate the capability of theweakest RF power amplifier. This action requires a variation in requiredinput signals to each RF power amplifier to avoid transmission powerlosses. Additionally, the voltage transient response associated withmultiple scattered capacitances is often more sluggish than desired.Therefore, improvements in this area would prove beneficial to the art.

SUMMARY

Embodiments of the present disclosure provide a distributed powerconverter and a method of operating a distributed power converter. Inone embodiment, the distributed power converter is for use with an RFpower amplifier and includes a primary converter connected to an inputvoltage and configured to provide a regulated DC intermediate voltagethat is galvanically isolated from the input voltage. Additionally, thedistributed power converter also includes a secondary regulatorconnected galvanically to the regulated DC intermediate voltage andconfigured to generate a regulated DC supply voltage for at least aportion of the RF power amplifier.

In another aspect, the method of operating a distributed power converteris for use with an RF power amplifier and includes providing a regulatedDC intermediate voltage that is galvanically isolated from an inputvoltage and generating a regulated DC supply voltage for at least aportion of the RF power amplifier that is galvanically connected to theregulated DC intermediate voltage.

The foregoing has outlined preferred and alternative features of thepresent disclosure so that those skilled in the art may betterunderstand the detailed description of the disclosure that follows.Additional features of the disclosure will be described hereinafter thatform the subject of the claims of the disclosure. Those skilled in theart will appreciate that they can readily use the disclosed conceptionand specific embodiment as a basis for designing or modifying otherstructures for carrying out the same purposes of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, referenceis now made to the following descriptions taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates a diagram of an embodiment of a distributed powerconverter for use with a plurality of RF power amplifiers constructedaccording to the principles of the present disclosure;

FIG. 2 illustrates a schematic of an example of an isolated powerconverter as may be employed as a primary converter in the distributedpower converter of FIG. 1;

FIG. 3 illustrates a schematic of a non-isolated regulator as may beemployed as a secondary regulator in the distributed power converter ofFIG. 1;

FIG. 4 illustrates a diagram of an additional embodiment of adistributed power converter for use with a plurality of RF poweramplifiers constructed according to the principles of the presentdisclosure;

FIG. 5 illustrates a diagram of another embodiment of a distributedpower converter for use with a plurality of RF power amplifiersconstructed according to the principles of the present disclosure; and

FIG. 6 illustrates a flow diagram of an embodiment of a method ofoperating a power converter carried out in accordance with theprinciples of the present disclosure.

DETAILED DESCRIPTION

Wireless base station RF power amplifier assemblies, using a singlevoltage source to power multiple RF final amplifier stages, suffer frominefficiency due to the inability to individually control a static DCvoltage level provided to each RF amplifier and a dynamic change in thisDC voltage level to allow for envelope tracking.

Gain of RF final power amplifier transistors may vary significantly dueto several factors including manufacturing variations and local ambienttemperature. The DC voltage source for the RF amplifier may be adjustedto allow a given final stage to deliver an intended RF output power witha required linearity. A single source of DC supply voltage is requiredto be high enough to allow the RF final amplifier stage with the weakestgain to deliver its intended RF output power and linearity. Thisrequirement typically causes the DC voltage level on other RF poweramplifier stages to be excessively high, leading to more losses andinefficiency.

Migration to a digital wireless standard has caused increased peak toaverage power ratios in RF final stages. The voltage supply to the finalpower amplifier stage is required to be high enough to support its peakpower requirement. However, for most of the time, the RF power level ismuch lower, and the RF final stage experiences high losses due to anexcessively high voltage supply. A single isolated power converter maynot be dynamically adjustable to lower voltages unless all RF finalstages are operating at their lower power conditions. Additionally,isolated power converters are typically not transiently responsiveenough to accurately track a desired output envelope of an RF finalstage.

Embodiments of the present disclosure provide DC power to the RF poweramplifier or its various stages using a fixed duty cycle isolated DC/DCconverter that is followed by one or more DC/DC regulators. Multiplefinal RF voltage levels may be generated that provide independent supplyvoltage setting and control to allow individual RF power amplifierefficiency enhancements. This leads to improvements in RF poweramplifier cost and physical volume considerations, as well.

FIG. 1 illustrates a diagram of an embodiment of a distributed powerconverter for use with a plurality of RF power amplifiers, generallydesignated 100, constructed according to the principles of the presentdisclosure. In the illustrated embodiment, the distributed powerconverter 100 may be employed in a cellular base station and includes aprimary converter 105, and a plurality of secondary regulator units 110a-110 n wherein a secondary regulator unit 110 a is typical. Thesecondary regulator unit 110 a includes a secondary regulator 111 a, atrim module 112 a, a tune module 113 a, a filter capacitor C₁ and an RFpower amplifier 114 a having an input S₁ and an RF output 115 a.

The primary converter 105 employs an input 106 that is connected to aninput voltage V_(IN) and an output 107 that provides a regulated DCintermediate voltage V_(INT) galvanically isolated from the inputvoltage V_(IN). The secondary regulator 111 a is connected galvanicallyto the regulated DC intermediate voltage V_(INT) and generates aregulated DC supply voltage V_(sup) for at least a portion of the RFpower amplifier 114 a. In an alternative embodiment, the portion of theRF power amplifier 114 a may be a final RF amplifier stage of the RFpower amplifier 114 a.

The input DC voltage V_(IN) from a base station mains or battery sourceis received at the primary converter 105, which provides protection fromsource disturbances and galvanically isolates the input source from theplurality of secondary regulator units 110 a-110 n receiving theregulated DC intermediate voltage V_(INT). The primary converter 105operates at a fixed duty cycle of about 50 percent to continuouslytransfer power from its input to its output and achieve a very highefficiency.

The regulated DC intermediate voltage V_(INT) from the primary converter105 is approximately equal to the input voltage V_(IN) when the sourceis in a range of about 36VDC-72VDC, as is typical for nominal 48VDCwireless base stations. The regulated DC intermediate voltage V_(INT) isapproximately doubled when the source is a range of about 18VDC-36VDC,as is typical for nominal 24VDC wireless base stations. Use of a higheroutput voltage value allows for diode rectification and is necessary forstep down load converters to provide 16V to 32V outputs used by the RFpower amplifier 114 a. Changes in the input DC voltage V_(IN) causes arelatively equal change to the regulated DC intermediate voltageV_(INT).

The regulated DC intermediate voltage V_(INT) is delivered to thesecondary regulator 111 a, which is a non-isolated buck regulator inthis embodiment. The secondary regulator 111 a provides a steady,regulated DC supply voltage V_(S) during changes to the input voltageV_(IN). A value of the regulated DC supply voltage V_(S) from thesecondary regulator 111 a may be individually adjusted employing thetrim module 112 a to meet the individual requirements of the RF poweramplifier 114 a.

The trim module 112 a provides a variable duty cycle for the secondaryregulator 111 a and a corresponding variation in the value of theregulated DC supply voltage V_(S). This action provides for a moreoptimum efficiency and gain variation linearity of the RF poweramplifier 114 a. The trim module 112 a also provides a reduced value ofthe regulated DC supply voltage V_(s) during an idle time of at leastthe portion of the RF power amplifier 114 a to which it is applied,thereby allowing for greater overall efficiency.

Additionally, the transient response may be optimized via the tunemodule 113 a corresponding to different values of the filter capacitorC₁ thereby providing voltage transient control for the RF poweramplifier 114 a. Examples of such a transient response circuit aredescribed in U.S. Pat. No. 7,432,692 B2 titled “Circuit and Method forChanging Transient Response Characteristics of a DC/DC Converter Module”by Thomas G. Wang, Vijayan J. Thottuvelil and Cahit Gezgin issued onOct. 7, 2008, which is incorporated by reference herein in its entirety.

FIG. 2 illustrates a schematic of an example of an isolated powerconverter, generally designated 200, as may be employed as a primaryconverter in the distributed power converter 100 of FIG. 1. The isolatedpower converter 200 includes an input capacitor C_(IN), first and secondpairs of switches S1, S2 and S3, S4, an isolation transformer T havingprimary and secondary windings N_(P), N_(S), a bridge rectifierconsisting of diodes D1, D2, D3, D4 and an output capacitor C_(OUT). Theisolated power converter 200 receives a DC input voltage V_(IN) andprovides a regulated DC output voltage V_(OUT), which may be employed asthe regulated DC intermediate voltage V_(INT) discussed with respect toFIG. 1.

The input voltage V_(IN) is applied to the primary winding N_(P) of theisolation transformer T via first and second pairs of switches S1, S2and S3, S4 operating alternatively with about a percent fixed dutycycle. This produces an alternating current (AC) waveform across theisolation transformer T having a peak value of about twice the input DCvoltage V_(IN). If a turns ratio of the isolation transformer T is 1:1,the secondary winding N_(S) delivers an AC waveform of twice the inputvoltage V_(IN) (at a 50 percent duty cycle), which is then rectified bythe bridge rectifier to an amplitude of the DC output voltage V_(OUT)equal to the input voltage V_(IN). If the turns ratio is 2:1, thesecondary AC voltage is four times the input voltage V_(IN) (for a 50%duty cycle), which provides an amplitude of the DC output voltageV_(OUT) equal to twice the input voltage V_(IN).

FIG. 3 illustrates a schematic of a non-isolated regulator, generallydesignated 300, as may be employed as a secondary regulator in thedistributed power converter 100 of FIG. 1. The non-isolated regulator300 includes an input capacitor C_(IN), first and second switches S1,S2, an inductor L and an output capacitor C_(our). The non-isolatedregulator 300 receives a DC input voltage V_(IN) and provides a DCoutput voltage V_(OUT), which corresponds to the regulated DC supplyvoltage V_(s) as discussed with respect to FIG. 1.

The DC input voltage V_(IN) is applied to the inductor L through thefirst switch S1 with a duty cycle of D. When the first switch S1 isclosed, the DC input voltage V_(IN) causes current to increase in theinductor L proportional to its inductance value and the amplitude of theDC input voltage V_(IN). The second switch S2 operates with a duty cycleof 1-D and out of phase with the first switch S1. That is, when thefirst switch S1 opens, the second switch S2 closes. This ensures thatthe inductor L always has a path for current flow.

When the first switch S1 is closed, current through the inductor L isincreasing proportional to values of the output capacitor C_(OUT) and aload across the DC output voltage V_(OUT) (not shown in FIG. 3). Whenthe second switch S2 is closed, current through the inductor L isdecreasing proportional to the values of the load and the outputcapacitor C_(OUT). The relationship between the DC input voltage V_(IN)and the DC output voltage V_(OUT) may be expressed by V_(OUT)=DV_(IN),where D is the duty cycle of the first switch S1. The value of D isadjusted to provide a required value of the DC output voltage V_(OUT).Absence of a coupling transformer allows the non-isolated regulator 300to provide an improved transient response to required changes in its DCoutput voltage V_(OUT) compared to employing transformer coupling suchas the isolated power converter 200 of FIG. 1.

FIG. 4 illustrates a diagram of an additional embodiment of adistributed power converter for use with a plurality of RF poweramplifiers, generally designated 400, constructed according to theprinciples of the present disclosure. The distributed power converter400 may also be employed in a cellular base station and includes aprimary converter 405, and a plurality of secondary regulator units 410a-410 n wherein a secondary regulator unit 410 a is typical. The primaryconverter 405 employs an input 406 that is connected to an input voltageV_(IN) and an output 407 that provides a regulated DC intermediatevoltage V_(INT) galvanically isolated from the input voltage V_(IN).

The secondary regulator unit 410 a includes a first secondary regulator411 a employing a trim module 412 a and a tune module 413 a as before, afilter capacitor C_(F1) and a final RF amplifier stage 414 a having anRF output 415 a. The first secondary regulator 411 a is connectedgalvanically to the regulated DC intermediate voltage V_(INT) andgenerates a first regulated DC supply voltage V_(s) for the final RFamplifier stage 414 a.

The secondary regulator unit 410 a also includes a second secondaryregulator 421 a employing a trim module 422 a and a tune module 423 a, afilter capacitor C_(P1) and a preamplifier stage 424 a having an inputS1 and a preamplifier output 425 a connected to the final RF amplifierstage 414 a. In the illustrated embodiment, the preamplifier stage 424 amay be an RF preamplifier stage or an intermediate frequency (IF)preamplifier stage. The second secondary regulator 421 a is connectedgalvanically to the regulated DC intermediate voltage V_(INT) andgenerates a second regulated DC supply voltage V_(SADD) for thepreamplifier stage 424 a.

General operation of the distributed power converter 400 reflects thatdiscussed with respect to the FIGS. 1, 2 and 3 above. However, thedistributed power converter 400 provides the second regulated DC supplyvoltage V_(SADD) that may be modified independently of the firstregulated DC supply voltage V_(S).

FIG. 5 illustrates a diagram of another embodiment of a distributedpower converter for use with a plurality of RF power amplifiers,generally designated 500, constructed according to the principles of thepresent disclosure. The distributed power converter 500 may also beemployed in a cellular base station and includes a primary converter505, and a plurality of secondary regulator units 510 a-510 n wherein asecondary regulator unit 510 a is typical. The primary converter 505employs an input 506 that is connected to an input voltage V_(IN) andfirst and second outputs 507, 508 that correspondingly provide first andsecond regulated DC intermediate voltages V_(INT1), V_(INT2)galvanically isolated from the input voltage V_(IN) and from each other.

The secondary regulator unit 510 a includes a first secondary regulator511 a employing a trim module 512 a and a tune module 513 a as before, afilter capacitor C_(F1) and a final RF amplifier stage 514 a having anRF output 515 a. The first secondary regulator 511 a is connectedgalvanically to the first regulated DC intermediate voltage V_(INT1) andgenerates a first regulated DC supply voltage V_(S) for the final RFamplifier stage 514 a.

The secondary regulator unit 510 a also includes a second secondaryregulator 521 a employing a trim module 522 a and a tune module 523 a, afilter capacitor C_(P1) and a preamplifier stage 524 a having an inputS1 and a preamplifier output 525 a connected to the final RF amplifierstage 514 a. In the illustrated embodiment, the preamplifier stage 524 amay be an RF preamplifier stage or an intermediate frequency (IF)preamplifier stage, as before. The second secondary regulator 521 a isconnected galvanically to the second regulated DC intermediate voltageV_(INT2) and generates a second regulated DC supply voltage V_(SA) forthe preamplifier stage 524 a. This second regulated DC supply voltageV_(SA) is galvanically isolated from both the input voltage V_(IN) andthe first regulated DC supply voltage V_(S) as may be advantageouslyrequired in some applications.

General operation of the distributed power converter 500 reflects thatdiscussed with respect to the FIGS. 1, 2 and 3. However, the isolatedpower converter 200 requires another transformer secondary windingfeeding a second output circuit to provide the second regulated DCintermediate voltage V_(INT2) for the second secondary regulator 521 aand generate the second regulated DC supply voltage V_(SA) that isisolated.

FIG. 6 illustrates a flow diagram of an embodiment of a method ofoperating a power converter, generally designated 600, carried out inaccordance with the principles of the present disclosure. The method 600is for use with an RF power amplifier and starts in a step 605. Then, ina step 610, a regulated DC intermediate voltage that is galvanicallyisolated from an input voltage is provided. The regulated DCintermediate voltage is provided through a fixed duty cycle conversion.

A regulated DC supply voltage for at least a portion of the RF poweramplifier is generated that is galvanically connected to the regulatedDC intermediate voltage, in a step 615. The regulated DC supply voltageis generated through a variable duty cycle regulation process wherein areduced value of the regulated DC supply voltage may be generated duringan idle time of at least the portion of the RF power amplifier, whichmay include a final RF amplifier stage.

A first decisional step 620 determines if an additional non-isolated DCregulated supply voltage is to be generated. If the additionalnon-isolated DC regulated supply voltage is not to be generated, themethod 600 proceeds to a second decisional step 625 which determines ifanother isolated regulated DC supply voltage is to be generated. Ifanother isolated regulated DC supply voltage is not to be generated themethod 600 ends in a step 630.

If the first decisional 620 determines that an additional non-isolatedDC regulated supply voltage is to be generated, the method 600 proceedsto a step 635. In the step 635, the additional non-isolated regulated DCsupply voltage is generated that is galvanically connected to theregulated DC intermediate voltage. The method 600 then proceeds to thesecond decisional step 625 which determines if another isolatedregulated DC supply voltage is to be generated. If again, anotherisolated regulated DC supply voltage is not to be generated the method600 ends in a step 630.

If the second decisional step 625 determines that another isolatedregulated DC supply voltage is to be generated, the method 600 proceedsto a step 640. In the step 640, another isolated regulated DCintermediate voltage is provided that is galvanically isolated from theinput voltage and the regulated DC intermediate voltage. Then, in a step645, another isolated and regulated DC supply voltage is generated thatis galvanically connected to the another isolated and regulated DCintermediate voltage. Both the additional non-isolated regulated DCsupply voltage and the another isolated regulated DC supply voltage maybe generated for a preamplifier stage of the RF power amplifier. Themethod again ends in the step 630.

While the method disclosed herein has been described and shown withreference to particular steps performed in a particular order, it willbe understood that these steps may be combined, subdivided, or reorderedto form an equivalent method without departing from the teachings of thepresent disclosure. Accordingly, unless specifically indicated herein,the order or the grouping of the steps are not limitations of thepresent disclosure.

Those skilled in the art to which the disclosure relates will appreciatethat other and further additions, deletions, substitutions andmodifications may be made to the described example embodiments withoutdeparting from the disclosure.

1. A distributed power converter for use with an RF power amplifier,comprising: a primary converter connected to an input voltage andconfigured to provide a regulated DC intermediate voltage that isgalvanically isolated from the input voltage; and a secondary regulatorconnected galvanically to the regulated DC intermediate voltage andconfigured to generate a regulated DC supply voltage for at least aportion of the RF power amplifier.
 2. The converter as recited in claim1 wherein the primary converter is a fixed duty cycle converter.
 3. Theconverter as recited in claim 1 wherein the secondary regulator is avariable duty cycle regulator.
 4. The converter as recited in claim 1wherein the secondary regulator provides a reduced value of theregulated DC supply voltage during an idle time of at least the portionof the RF power amplifier.
 5. The converter as recited in claim 1wherein the secondary regulator generates the regulated DC supplyvoltage for a final RF amplifier stage of the RF power amplifier.
 6. Theconverter as recited in claim 1 further comprising an additionalsecondary regulator connected galvanically to the regulated DCintermediate voltage and configured to generate an additional regulatedDC supply voltage.
 7. The converter as recited in claim 6 wherein theadditional secondary regulator provides the additional regulated DCsupply voltage to a preamplifier stage of the RF power amplifier.
 8. Theconverter as recited in claim 1 further comprising the primary converterconfigured to provide another regulated DC intermediate voltage that isgalvanically isolated from the input voltage and the regulated DCintermediate voltage.
 9. The converter as recited in claim 8 furthercomprising another secondary regulator connected galvanically to theanother regulated DC intermediate voltage and configured to generateanother regulated DC supply voltage.
 10. The converter as recited inclaim 9 wherein the another secondary regulator generates the anotherregulated DC supply voltage for a preamplifier of the RF poweramplifier.
 11. A method of operating a distributed power converter foruse with an RF power amplifier, comprising: providing a regulated DCintermediate voltage that is galvanically isolated from an inputvoltage; and generating a regulated DC supply voltage for at least aportion of the RF power amplifier that is galvanically connected to theregulated DC intermediate voltage.
 12. The method as recited in claim 11wherein providing the regulated DC intermediate voltage employs a fixedduty cycle conversion.
 13. The method as recited in claim 11 whereingenerating the regulated DC supply voltage employs a variable duty cycleregulation.
 14. The method as recited in claim 11 wherein generating theregulated DC supply voltage includes generating a reduced value of theregulated DC supply voltage during an idle time of at least the portionof the RF power amplifier.
 15. The method as recited in claim 11 whereingenerating the regulated DC supply voltage includes generating theregulated DC supply voltage for a final RF amplifier stage of the RFpower amplifier.
 16. The method as recited in claim 11 whereingenerating the regulated DC supply voltage further comprises generatingan additional regulated DC supply voltage that is galvanically connectedto the regulated DC intermediate voltage.
 17. The method as recited inclaim 16 wherein the additional regulated DC supply voltage is generatedfor a preamplifier stage of the RF power amplifier.
 18. The method asrecited in claim 11 wherein providing the regulated DC intermediatevoltage further comprises providing another regulated DC intermediatevoltage that is galvanically isolated from the input voltage and theregulated DC intermediate voltage.
 19. The method as recited in claim 18wherein generating the regulated DC supply voltage further comprisesgenerating another regulated DC supply voltage that is galvanicallyconnected to the another regulated DC intermediate voltage.
 20. Themethod as recited in claim 19 wherein the another regulated DC supplyvoltage is generated for a preamplifier stage of the RF power amplifier.